Fun: RPS cheater

Let's make a rock-paper-scissors game, where the computer always wins. You can try it

The program uses the GET parameter pick to get the user's choice. If pick isn't there...

rock-paper-scissors.php

... the program prints a welcome message:

No parameter

If there's a user pick...

rock-paper-scissors.php?pick=paper

... the program shows the user's pick, and one of its own. Thing is, it always wins.

Computer wins

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Making a choice

Here's the first part of the program:

  1. <?php
  2. $userPick = null;
  3. $computerPick = null;
  4. if (isset($_GET['pick'])) {
  5.     $userPick = $_GET['pick'];
  6.     if ($userPick == 'rock') {
  7.         $computerPick = 'paper';
  8.     }
  9.     if ($userPick == 'paper') {
  10.         $computerPick = 'scissors';
  11.     }
  12.     if ($userPick == 'scissors') {
  13.         $computerPick = 'rock';
  14.     }
  15. }
  16. ?>

The variables $userPick and $computerPick record the user's and computer's pick. They start off as null. That's how the program will know whether it needs to output the welcome text.

If there is a value for pick (line 4), the code grabs it, and puts it into $userPick (line 5). Then it makes its own choice. It will take whatever beats the user.

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Showing the results

The rest of the program tells the user what happened.

  1. <h1>Rock, paper, scissors</h1>
  2. <?php
  3. if ($userPick == null) {
  4.     print "<p class='welcome'>Welcome!</p>";
  5. }
  6. else
  7. {
  8.     print "<p>Your pick: $userPick</p>\n";
  9.     print "<p>My pick: $computerPick</p>\n";
  10.     print "<p class='lose'>Sorry, you lose!</p>\n";
  11. }
  12. ?>
  13. <p>Click on your choice.</p>
  14. <p>
  15.     <a class="pick" href="rock-paper-scissors.php?pick=rock">
  16.         <img src="rock.png" alt="Rock">
  17.     </a>
  18.     <a class="pick" href="rock-paper-scissors.php?pick=paper">
  19.         <img src="papers.png" alt="Paper">
  20.     </a>
  21.     <a class="pick" href="rock-paper-scissors.php?pick=scissors">
  22.         <img src="scissors.png" alt="Scissors">
  23.     </a>
  24. </p>

First, the code decides whether to show the welcome message. It will do that if $userPick is MT.

  • if ($userPick == null) {
  •     print "<p class='welcome'>Welcome!</p>";
  • }
  • else
  • {

If $userPick isn't null, then the program shows the two picks, and who won:

  • print "<p>Your pick: $userPick</p>\n";
  • print "<p>My pick: $computerPick</p>\n";
  • print "<p class='lose'>Sorry, you lose!</p>\n";

There's no need for an if to detect who won. The computer always wins.

Finally, the program shows the three choices, for the next game:

  • <p>Click on your choice.</p>
  • <p>
  •     <a class="pick" href="rock-paper-scissors.php?pick=rock">
  •         <img src="rock.png" alt="Rock">
  •     </a>
  •     <a class="pick" href="rock-paper-scissors.php?pick=paper">
  •         <img src="papers.png" alt="Paper">
  •     </a>
  •     <a class="pick" href="rock-paper-scissors.php?pick=scissors">
  •         <img src="scissors.png" alt="Scissors">
  •     </a>
  • </p>

Notice the hrefs for the links. The value of the pick that matches the image is at the end of the URL.

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Easy peasy

That's it! See how easy it is for a computer to cheat? We could make it less obvious, by cheating on, say, one game in four.

Yeah, online gambling's legit, right? What could possibly go wrong?